A number of devices are known for the chemical analysis of substances in liquids, especially biological liquids. One type of device requires expensive equipment, highly trained operators and a large volume of samples for analysis.
Another type of device is a relatively simple, portable, multilayer element for carrying out a single test at a time without expensive equipment.
U.S. Pat. No. 3,723,064, issued Mar. 23, 1973, is directed to a layered testing device comprising a layer impregnated with a chemical reagent for a reaction with the substance under test comprising a permeable member having first and second regions of different permeabilities to the test fluid. A transmission layer is placed adjacent the permeable member to aid in drawing the reaction products resulting from the reaction of the chemical reagent and the substance under test through to the next layer, which is an indicator layer, impregnated with a chemical adapted to react with the above-mentioned reaction products to produce a visual reaction indicative of the presence and concentration of the substance under test.
U.S. Pat. No. 3,992,158, issued Nov. 16, 1976, discloses an integral analytical element containing a spreading layer and a reagent layer. The spreading layer is an isotropically, non-fibrous porous layer which spreads within itself at least a component of the applied liquid sample to obtain a uniform concentration which then passes into the adjacent reagent layer where it can react to form a detectable species.
U.S. Pat. No. 4,042,335, issued Aug. 16, 1977, is directed to a multilayer element for the analysis of liquids such as biochemical and biological liquids. The element comprises a reagent layer which includes a composition that is interactive with the substance to be analyzed to provide a diffusible, detectable species; and a registration layer that is permeable to the detectable species and within which such species can be detected. The element can also include a spreader layer and a radiation blocking layer to enhance detection of the detectable species.
U.S. Pat. No. 4,050,898, issued Sept. 27, 1977, is directed to an analytical element comprising at least two superposed layers, a spreading layer and reagent layer, wherein the spreading layer is a non-fibrous, isotropically porous spreading layer of water-resistant material which includes a non-ionic surfactant to normalize transport in the spreading layer.
U.S. Pat. No. 4,066,403, issued Jan. 3, 1976 is directed to an integral analytical element for analyzing complex fluids which comprises a first reagent for reacting with an analyte to produce a decomposition product and a second reagent adapted to react with said decomposition product to produce a detectable change wherein a barrier to said decomposition product is disposed between the first and second reagents which is substantially impermeable to interferants.
U.S. Pat. No. 4,069,016, issued Jan. 17, 1978, is directed to a method for determining bilirubin in an aqueous liquid sample which comprises contacting said sample with a composition containing a diffusible, bilirubin-displaceable, detectable ligand bound to a carrier which can also bind bilirubin, and detecting the thus-displaced detectable ligand.
U.S. Pat. No. 4,144,306, issued Mar. 13, 1979, is directed to a displacement/release method employing a multilayer analytical element comprising at least a reagent layer and a registration layer wherein the reagent layer contains an interactive composition including a non-diffusible material having a preformed detectable moiety bound thereto, which composition, in the presence of a liquid containing an analyte, provides a diffusible product comprising the preformed detectable moiety by displacement by the analyte. The registration layer receives the diffusible product. Other layers may also be employed, including supports, spreader layers, radiation blocking layers, and the like. As an example of said interactive composition, mention is made of a tagged antigen-antibody complex wherein the analyte displaces the tagged member which migrates to the registration layer.
U.S. Pat. No. 4,166,093, issued Aug. 28, 1979, is directed to an element for the analysis of liquids which include a radiation-transmissive reagent layer containing a composition interactive with an analyte to provide a radiometrically detectable species, a porous radiation blocking layer permeable to the analyte and a radiation-transmissive, detectable species migration inhibiting layer interposed between the reagent layer and the radiation-blocking layer, said detectable species migration-inhibiting layer being permeable to said analyte and inhibiting the migration of said radiometrically detectable species to said porous radiation blocking layer upon contact of said element with the liquid under analysis.
U.S. Pat. No. 4,258,001, issued Mar. 24, 1981, is directed to a multilayer element for competitive immunoassay which includes a zone having a particulate structure which comprises heat-stable, non-swellable organo-polymeric particles and an adhesive. An immunoreagent, such as a fluorescent-labelled antigen, may be bound to the particles. In Example 50, a competitive immunoassay element is described wherein an antibody is immobilized in a spreading/reagent zone dispersion and labeled antigen is premixed before application to the test element. It is also stated that the labelled antigen may be incorporated into the element. However, it is stated (col. 30, lines 2 to 7) that where the labelled antigen is incorporated in the element, care should be taken to maintain the labelled antigen apart from the immobilized antibody which is also in the element to avoid premature binding of labelled antigen to antibody.
Immunochemistry, D. M. Weir, Third Edition, Blackwell Scientific Publication, Oxford, England, Vol. 1, Chapter 19, describes a radial, quantitative immunoprecipitation technique wherein an analyte containing an antigen is placed in the center of a layer of colloid containing an antibody. The distance the antigen radiates from the center is measured to provide a quantitative determiation of the antigen in the analyte.
European Patent Application No. 0 051 183, filed Oct. 15, 1981 discloses a multilayer analysis element comprising a porous medium layer to which an antigen (or antibody) is immobilized and a layer through which substances which did not participate in the immunoprecipitation in the porous medium layer can diffuse, whereupon detection means can be employed to determine the quantity of said substances. In operation, an antigen (or antibody) to be analyzed for is labelled and then applied to the porous medium layer. The labeled antigen (or antibody) reacts with the immobilized antibody (or antigen) to form a complex. Excess, unreacted antigen (or antibody) is inherently separated from the complex and diffused into the reagent layer. Unreacted labelled antigen (or antibody) is optically measured to provide a quantitative determination. This patent application demonstrates the quantitative nature of gel-mediated precipitation reactions.